Mercury switch



Lutin March 5, 1957 E. R. COUTANT 2,784,279

MERCURY SWITCH Filed Aug. so, 1954 F3 O F/g/ Fgz MERCURY SWITCH Edward R. Contant, Stratford, Conn., assignor to General Electric Company, a corporation of New York Application August 30, 1954, Serial No. 452,961

3 Claims. (Cl, 200-152) This invention relates to electric switches and in particular to a new type mercury button switch.

By mercury button switch is meant that type of electrical switching device containing one or more mercury buttons rotatable to an on or off position. Conventionally a mercury button comprises a pair of metallic shells separated by an insulating barrier having a passageway therein. A glass ring is used to form a seal between the shells while insulating them from each other. When the metal shells and barrier are rotated to a predetermined position, mercury stored between each shell and the barrier passes through the passageway in the barrier to establish electrical contact between the shells and thereby act as a switching device. The mercury buttons used herein are of a conventional type as described, for example, in U. S. Patent 2,101,092 which is assigned to the same assignee as is the present invention.

This invention is primarily concerned with a fourway mercury switch having a split enclosure comprising a base and cover of insulating material. When it is necessary to control, for instance, a lighting load from more than two points, a three-way switch is used at the point nearest the power source, another at the point near the light, and fourway switches are used at each other point. A four-way mercury switch contains four mercury button switches, and electrical contact for connecting the buttons in the electrical circuit is made generally between the button shells and external pressure contacts at the sides of the buttons with the pressure contacts being located approximately at the geometric center of rotation of each of the buttons. Such a contact arrangement within a switch of normal household size limits the spring pressure that can be used, the area of contact and, hence, the load carrying capacity of the switch.

The contact strips of the present invention are held in place by both the base and the cover so that the contacts will not be distorted when the terminal screws are tightened to clamp a lead wire thereto. The present switch has a relatively shallow base in which the contacts and buttons are iirst assembled. The outer contacts extend upwardly from the mating surface of the base so that when the cover is removed the spring pressure of the inner contacts tends to are the outer contacts over the side walls of the base. When the cover is placed over the base and fastened thereto the outer contacts are necessarily forced towards each other and held in compression by the cover. Because of the increased contactv pressure between the contact strips and the mercury buttons, this switch has been given a rating with a higher load carrying capacity by the Underwriters Laboratories, Inc. than any fourway mercury switch heretofore known. The subject switch has also been provided with a back wiring feature in order to utilize to the best advantage the available wiring space in the conventional size switch box. This back wiring feature incorporates enclosed terminal screws which have prevented short circuits from occurring between vthe nited Statesv Patent y terminal screws and the inside walls ,of the switch box.A

"C 2,784,279 luatemnted Mar. 5, 1957 This diiiiculty has long plagued the industry and it has only been minimized'in the past by providing thin iiber plates with each four-way mercury switch to insulate the terminal screws from the inner walls of the box.

Also, the switch parts are not permanently fastened to the switch housing but are held in place by the cooperation of the base and cover; therefore, the switch can be disassembled and reassembled with ease if a minor fault is found in any switch part during the testing thereof so that the entire switch need not be discarded but may be repaired and put back into use with a consequent saving in scrap material. Also, the outer top and bottom edges of the base of the present switch are cut back in order to allow more space for accommodating the bending and twisting of the wires which are to be connected with the switch in a switch box.

Accordingly, it is a principal object of this invention to provide a four-way mercury button switch with an improved contact arrangement for engaging the mercury button so as to increase the load carrying capacity of the switch.

It is a further object of this invention to increase the contact pressure between the contacts and the shells of the mercury buttons in a four-way mercury switch.

It is a further object of this invention to provide a totally enclosed split housing for a four-way mercury switch comprising a recessed base and a recessed cover.

It is a further object of this invention to provide a fourway mercury switch with contacts which are held in place by both the base and the cover so that they will not be distorted when the binding screws are tightened.

It is a further object of this invention to provide a fourway mercury switch of compact design so that a maximum wiring space will be available in the switch box.

It is a still further object of this invention to provide a four-way mercury switch with a back wiring feature so that the terminal screws are recessed to prevent shorting across to the inside walls of a switch box.

Further objects and advantages of this invention will become apparent and the invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing:

Figure 1 is a front elevational View of a four-way mercury switch embodying my invention.

Figure 2 is a right side view of the switch of Figure 1 with both views showing the clearance between the switch housing and the inner walls of a switch box.

Figure 3 is a cross-sectional side elevational view taken on the lines 3 3 of Figure 1.4

Figure 4 is a top plan View of the base of the switch housing embodying my invention with the inner and outer contacts in place while the mercury buttons are shown in dotted lines to illustrate their relative locations` Figure 5 is a bottom plan view of Figure 4.

Figure 6 is a cross-sectional side elevational View taken substantially along the lines 6 6 of Figure l with the contacts shown in full lines.

Figure 7 is a partial exploded view showing the arrangement of the outer contacts when the recessed cover is removed from the base.

Figure 8 is a partial sectional end view taken generally from the cover for the manual operation of the switch. A sheet metal mounting strap 14 is fastened across the face of the cover 11 by the screws 15 which are also used to hold the cover assembled with the base. The mounting strap is provided at either end with an elongated aperture 16 for the reception of screws (not shown) for fastening the switch 1h in a conventional switch box. The four corners of the strap 14 are provided with mounting ears 17 which are scored so that they may be readily removed and used as washers under certain conditions which are well understood in this art.

The present invention is primarily concerned with the two-piece switch housing and the internal switch parts now to be described. Referring now to Figures 4 and 6 it is seen that the recessed base 12 has a dee central cavity 2t) for receiving the mercury buttons and four shallow recesses 21 arranged at the four corners of the base. The upper surface 18 of the base 12 is flat so that the top and bottom outer edges of the base 12 are cut out as at 19 to provide more wiring space at the back of the switch. Four contact strips are located in the switch base 12. There are two outer contacts 22 and two inner contacts 23. The main portion of each of the outer contacts 22 is` arranged along the inner side wall of the base 12 with its inner end supported on the abutment 24. The terminal end 25 of the outer contacts 22 is seated in the recess 21 of the base and it extends upwardly from the main body of the contact to be parallel with the end wall of the base 12.

As is seen in Figure 4, the terminal ends 25 of the outer contacts 22 are arranged side by side at the lower end of the switch housing. At this point it should be remembered that a mercury switch has only one top end and one bottom end for if it is not installed with the correct side upward the mercury button switches will fail to operate properly. Therefore, in Figure l the switch has been correctly placed so that hereinafter when reference is made to the top of the switch housing it will be known that this is a particular end of the housing and not one or the other of the ends of the housing. For this reason the word Top i-s marked on the mounting strap as is shown in Figure 1 so as to indicate the correct position of the switch. Going back to Figure 4, screws 26 are threaded into the terminal ends 25 of the outer contacts for supporting a locking nut 27 on the inner end thereof for a reason which will be explained later.

The inner contacts 23 are provided with terminal ends 28 which are arranged side by side in. the recesses 21 at the top end of the switch base 12. Looking at Figure 4, the left-hand inner contact 23 extends from the terminal end 28 down to the bottom wall of the cavity 20 in the base and under the mercury button 29 shown in dotted lines. The remainder of this contact is made as -a separate piece 30 which is welded to the abovedescribed portion at 31. The free end of the portion 30 is formed as an upwardly turned U-shaped formation 32 with parallel legs 33.

Again looking at Figure 4, the right-hand inner contact 23 also extends from the terminal end 2S downward to the bottom wall of the cavity 20 and under the mercury button 34 as is best shown in Figure 6. A separate portion 35 is welded at 36 to the remainder of the contact in a manner similar to the portion 39 of the other inner contact. The free end of the portion 35 is also formed as an upwardly turned U-shaped formation 37 having parallel legs 38. A pair of longitudinally spaced spherical trunnions 39 are formed on the inner surface of the outer contacts 22 to be in alignment with the spherical trunnions 40 formed on the outer surface of the legs 33 and 3S of the inner contacts 23. Thus, it will be seen that provision has been made in the base 12 for rotatably supporting four mercury switches; namely, the upper buttons 29 and 34 and lower buttons 41 and 42.

As was mentioned earlier, the switching action provided by this switch is' accomplished by the rotation of the mercury buttons. These buttons must be rotated simultaneously in order to obtain the proper action and for this purpose a slider mechanism 45, as is best shown in Figures 3 and 7, is arranged centrally of the switch housing between the U-shaped portions 32 and 37 of the inner contacts. The slider 4S comprises a pair of wide V-shaped links 46 of insulating material which are pivotally mounted as at 47 to the strut 4S. A pair of parallel links 5G are pivotally mounted as at 51 to the adjacent ends of the links 46. The end of each link Sil nearest the front face of the switch housing is provided with an overhanging arcuate bearing 52 at either side of the slider mechanism so as to overlie -a portion of the mercury buttons. It should be appreciated that a mercury button is shaped generally as a center-flanged wheel with tread-like portions at either side of the ilange. Since the buttons 29, 34, 41 and 42, as is seen in Figure 4, are arranged in a square pattern, it should be appreciated that the bearings 52 of the slider mechanism 45 are adapted to rest on the inner tread-like portion of the mercury buttons. A transverse groove 53 is formed in each tread-like portion of the mercury button so that engagement may be made between the bearings 52 and the mercury buttons as by the detent 54 formed on the end of each bearing 52. Only the inner grooves 53 of the mercury buttons are used in the present switch for effecting the movement of the buttons but grooves are Jformed on both sides of the buttons since the same buttons are used in single-pole mercury switches having use for both grooves.

When the switch is completely assembled, the strut t8 extends through the opening 60 in the cover 11. The distal end 61 of the strut 4S is of reduced cross section and a ber washer 62 is mounted thereon. A trigger 13 is mounted over the end 61 of the strut and is held thereon by a pair of cam members 63 arranged at either side of the trigger to cooperate with the detent spring 64 which is fixed to the under-side of the mounting strap 14 in a manner which is well understood in this art. The spring 64 serves to hold the bearings 52 of the slider mechanism 45 in contact with the mercury buttons as well as to lock the trigger in either the on or oil position against unwanted vibrating forces which might otherwise move the trigger and actuate the switch.

Turning now to Figure 6, it is seen that the base 12 is relatively shallow as compared with the cover 11 so that the plane through the rotating centers of the mercury buttons is substantially ush with the mating surface 18 of the base 12. To assemble the switch parts, the inner contacts 23 containing the terminal screws 26 and locking nut 27 are irst placed in the base 12 to lie between the dividing partition 71 formed on the bottom Wall of the cavity 20. The mercury buttons are then slipped into place and finally the outer contacts 22 are squeezed into the base 12 between the mercury buttons and the inner side walls of the base. Since only the lower portion of the outer contacts 22 is located in the base 12, the spring action of the arms 33 and 38 of the inner contacts 23 tends to flare the outer contacts outwardly over the side edges of the base as is best seen in Figure 7.

The cover 11 at the top and bottom ends thereof is formed with four terminal-screw windows 72 of arched construction to expose the terminal screws 26 to the outside of the switch housing. The inner walls of the windows 72 are notched as at 73 so that the notches engage over the terminal ends 25 of the outer contacts and the ends 28 of the inner contacts. In placing the cover 11 over the base 12, it is necessary to first press the terminals 25 and thus the outer contacts 22 inwardly so that the contacts will iit in the cover. By so doing, the spacing between the spherical trunnions 39 and 40 of the outer and inner contacts respectively is reduced to provide good electrical contact with the mercury buttons mounted therebetween.

A pair of wire-receiving openings 75 is formed through the back wall of the base 12 for each terminal end of the contacts so that there are eight openings in all. These openings are located in the cut-out portions 19 of the base, and the openings of each pair are spaced on either side of the terminal screws 26. In wiring this switch, the insulation from each conductor is stripped back about 3/1" and the bare wire is inserted through one of the openings 75 between the locking nut 27 and the terminal end of one of the contacts. By tightening the terminal screw 26, the locking nut compresses the bare wire against the contact for making a firm electrical connection.

Having described my invention of a new and improved four-way mercury switch, it will be readily appreciated by one skilled in this art that by using a split housing having a shallow base for holding the contacts and mercury buttons I have been able to increase the contact pressure between the contacts and buttons since the recessed cover assists in clamping the parts together. The base and cover also provide a total enclosure for the switch parts so that dust and other foreign matter are prevented from entering the interior of the switch. The low cut base also increases the ease of assembly of the parts and it contributes to the over-all compactness of the switch which is of necessity of large size. Because of the back wiring feature and the cut-outs at the top and bottom edges of the back wall of the base, it is relatively easy to wire the switch and force the switch into the ordinary switch box because of the increased wiring space between the back of the switch and the interior back wall of the box. Also, since the terminal ends of the contacts are depressed in the end walls of the cover member, there is no danger of short circuit between the terminal screws and the inner walls of the switch box. A further advantage of the present invention is that the switch parts are not permanently fastened in either the base or the cover so that it is an easy matter to disassemble and reassemble the switch in order to replace any defective parts that might be discovered.

Modifications of this invention will occur to those skilled in this art and it is to be understood, therefore, that this invention is not limited to the particular embodiment disclosed but that it is intended to cover all modications which are Within the true spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A four-way mercury switch comprising a housing of insulating material formed of a shallow base member and a recessed` cover member, inner contacts seated on the bottom wall of the base and outer contacts supported along the inner side walls of the base, said contacts serving to support a plurality of mercury buttons for rotation in the housing, the terminal ends of said contacts extending from the base upwardly into the cover at the opposite ends of the housing, the pivotal axes of said buttons lying substantially on the top face of said base, the inner contacts exerting a force against the mercury buttons and the outer contacts, this force tending to flare the outer contacts outwardly when the covei is removed from the base, so that when the cover is assembled the outer contacts are squeezed by the cover to provide good electrical connection between the mercury buttons and the contacts.

2. A mercury switch comprising an insulating housing with a shallow base member and a recessed cover member, inner contacts seated on the bottom wall of the base and outer contacts supported along the inner side Walls of the base, said contacts providing pivotal support means for a plurality of mercury buttons within the housing, the pivotal axes of said buttons lying substantially within the separating plane between the said base and cover member so that the switch contacts will be compressed by the said cover, the terminal ends of said contacts extending from the base into the cover member and being held fixed therein, the base being provided with wire-receiving openings through its bottom wall for receiving lead wires to be connected to said terminal ends of the contact, and terminal-screw windows in the ends of the cover member in which the terminal screws of the contacts are enclosed.

3. A mercury switch comprising an insulating housing with a shallow base member and a recessed cover member, contacts supported along the inner side walls of the base serving as the pivotal support means for at least one mercury button, the pivotal axis of said button lying substantially within the separating plane between the said base and cover member so that the switch contacts will be compressed by the said cover, the terminal ends of said contacts extending from the base upwardly into the cover at the opposite ends of the housing and being held fixed therein.

References Cited in the tile of this patent UNITED STATES PATENTS 2,142,151 Sambleson Ian. 3, 1939 

